1. Field of the Invention
The present invention relates to multiple frequency band (multiband) antennas, particularly compact multiband antennas for wireless communication devices (WCDs), such as cellular telephones, portable (laptop) computers, hand-held computers, and the like. In one practical embodiment, the present invention relates to UHF (ultra-high frequency) and SHF (super-high frequency) antennas for WCDs that provide operation in multiple frequency bands while having only a single feed point.
2. Description of Related Art
There is an increasing demand for wireless devices that are capable of communicating in multiple frequency bands. For example, a wireless device configured for the United States and European markets may require the ability to operate in four bands: the European cellular telephone band (880-960 MHz), the United States PCS band (1850-1990 MHz), the Bluetooth band (2.4-2.5 GHz) and the 802.11A unlicensed band (5.15-5.25 GHz).
Various multiband single feed line antennas are known in the art. Some are designed for use at HF or VHF and are configured so that they are unsuitable for reduction in size for use in a wireless device. Others, although UHF and/or SHF antennas designed for use in small spaces, are complex, do not readily permit more than two or three bands of operation, do not permit multiband operation without interaction among the bands, are unsuitable for implementation as conductive traces on a printed circuit board (PCB), and/or are expensive to manufacture.
Accordingly, there remains a need for multiband single feed antennas, particularly small multiband single feed UHF and SHF antennas suitable for use in wireless communication devices.
In a first aspect, the invention is directed to a multiband antenna operable in at least a first frequency band and a second frequency band higher in frequency than the first frequency band (the second frequency band need not be an odd multiple of the first frequency band). The multiband antenna includes a dipole having a first conductive leg and a second conductive leg and is adapted to be directly fed between the first and second legs. At least a portion of the first leg of the dipole has a meander configuration. The first leg has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) in the first frequency band and the second leg has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) or more in the first frequency band. The multiband antenna further includes a non-driven parasitically-excited conductive element closely spaced to the first dipole leg and electrically connected to the second dipole leg. The parasitic element has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) in the second frequency band.
In a preferred embodiment, the dipole legs and parasitic element are conductive traces on a thin dielectric such as a printed circuit board. Only a single dielectric layer is required. The traces can be on the same side of the printed circuit board and the antenna can also include either one or two further conductive traces on the other side of the printed circuit board. One of the further conductive traces, if present, is electrically connected to the second leg of the dipole and extends under at least a portion of the second leg, under at least a portion of the gap between the dipole legs, under a portion of the first leg, and under a portion of the parasitically-excited element. The other of the further conductive traces, if present, has no electrical connection to any other traces on the printed circuit board and extends under a portion of parasitic element and under a portion of the space between the first leg and the parasitically-excited element.
In a practical embodiment of the first aspect of the invention, the first frequency band is the 880-960 MHz band and the second band is the band of frequencies between 1850 MHz and 2.5 GHz that includes the 1850-1990 MHz band and the 2.4-2.5 GHz band. Such an antenna, having a wide second band, can be characterized as a three-band rather than a two-band antenna. The antenna dimensions can be scaled to provide operation in other frequency bands. For example, the first frequency band can be the 880-960 MHz band and the second frequency band can be the 1850-1900 MHz band or, the first frequency band can be the 1850-1900 MHz band and the second frequency band can be the 2.4-2.5 GHz band.). Scaling for yet other frequency bands is possible.
In a second aspect, the invention is directed to a multiband antenna operable in at least a first frequency band and a second frequency band higher in frequency than the first frequency band, (the second frequency band need not be an odd multiple of the first frequency band). The multiband antenna includes a dipole having a first leg and a second leg, and is adapted to be directly fed between the first and second legs. At least a portion of the first leg of the dipole has a meander configuration. The first leg has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) in the first frequency band and the second leg has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) or more in the first frequency band. The legs of the dipole can be conductive traces on the first side of a thin dielectric. Only a single dielectric layer is required. A further conductive trace can be located on the second side of the dielectric underneath a portion of the meander portion of the first leg. The further conductive trace has no connection to any other trace. The trace itself (not taking its proximity to the meandering dipole leg into account) has no resonance in the first and second frequency bands or any odd multiple thereof. The further conductive trace is shaped, sized and positioned under the meander portion so as to create an LC trap that electrically decouples the distal portion of the first leg when the antenna operates in the second frequency band such that the remaining portion of the first leg has an effective electrical length of about one-quarter wavelength (or an odd multiple thereof) in the second frequency band. The LC trap itself may or may not be resonant in the second frequency band.
In a practical embodiment, at least a portion of the meander-configured first leg portion folds back on itself at least twice and the further conductive trace is located underneath that portion of the first leg. The meander portion that folds back on itself at least twice can have three segments generally parallel to each other in which at least two of the segments are substantially linear.
In a practical embodiment of the second aspect of the invention, the first frequency band is the 880-960 MHz band and the second band is the 5.15-5.25 GHz band. The antenna dimensions and/or LC trap characteristics can be scaled to provide operation in other frequency bands. For example, the first frequency band may be the 880-960 MHz band and the second frequency band may be the 1850-1900 MHz band or, the first frequency band may be the 1850-1900 MHz band and the second frequency band may be the 2.4-2.5 GHz band.). Scaling for yet other frequency bands is possible.
In a third aspect, the invention is directed to a multiband antenna operable in at least a first frequency band, a second frequency band higher in frequency than the first frequency band (the second frequency band need not be an odd multiple of the first frequency band) and a third frequency band (the third frequency band need not be an odd multiple of the first frequency band or the second frequency band) higher in frequency than the first and second frequency bands. The multiband antenna includes a dipole having a first leg and a second leg, adapted to be directly fed between the first and second legs. At least a portion of the first leg of the dipole has a meander configuration and the first leg has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) in the first frequency band and the second leg has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) or more in the first frequency band. A non-driven parasitically-excited element is closely spaced to the first dipole leg and is electrically connected to the second dipole leg. The parasitic element has an electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) in the second frequency band. The dipole and the parasitically-excited element can be conductive traces on the same side of a thin dielectric. Only a single dielectric layer is required. A further conductive trace can be located on the second side of the printed circuit board underneath a portion of the meander configuration. The further conductive trace, if present, has no connection to any other trace and itself has no resonance in the first, second and third frequency bands or any odd multiple thereof. The further conductive trace is shaped, sized and positioned under the meander portion so as to create an LC trap that electrically decouples a portion of the first leg when the antenna operates in the third frequency band such that the remaining portion of the first leg has an effective electrical wavelength of about one-quarter wavelength (or an odd multiple thereof) in the third frequency band.
The various antennas according to aspects of the present invention can have flexible conductive traces and can be formed on a flexible dielectric so that they can be bent and formed to fit into and around various objects in a restricted space.
If desired, the various antennas according to aspects of the present invention can provide the same nominal feedpoint impedance for all the frequency bands in which they are intended to operate, thus requiring no matching networks.
A single antenna for operation in multiple bands in accordance with aspects of the present invention can have a lower cost than multiple antennas and few assembly configurations.
Antennas according to aspects of the present invention can be made of printed circuit board material, thus having low cost, high availability and high reliability.
Antennas according to aspects of the present invention can have a single RF feed point, thus allowing a single feedline and avoiding the higher cost of multiple feedlines.
Practical implementations of aspects of the present invention can achieve a voltage-standing-wave ratio (VSWR) of less than 2.5-1 in all bands in which the antenna is intended to operate. Efficient radiation may be achieved, therefore lowering battery consumption.
Antennas according to aspects of the present invention can have a low, very thin, small size, and light weight allowing it to be embedded in restricted areas of a laptop (notebook) computer, for example in the hinge region.